INGINERIE SOFTWARE

Ştefan Stăncescu

CURSUL 2.2

Legile lui Lehman.

INGINERIA SOFTWARE StSt 2

CURSUL 2.2- LEGILE LUI LEHMAN

I - Continuing Change

II - Increasing Complexity

III - Self Regulation

IV - Conservation of Organisational Stability

V - Conservation of Familiarity

VI - Continuing Growth

VII - Declining Quality

VIII - Feedback System

INGINERIA SOFTWARE StSt 3

CURSUL 2- LEGILE LUI LEHMAN

I - Continuing Change

A program that is used must be continually adapted else it becomes progressively less satisfactory

Un produs program software PPSW operational

trebuie continuu adaptat

altfel devine

din ce in ce mai putin eficient

(realitatea initiala la t=0 se modifica in t)

INGINERIA SOFTWARE StSt 4

CURSUL 2- LEGILE LUI LEHMAN

II - Increasing Complexity

As a program is evolved its complexity increases unless work is done to maintain or reduce it.

Daca un PPSWevolueaza

complexitatea sa creste

deci trebuiesc activitati de a

mentine sau reduce complexitatea

(termodinamica modificarilor – entropia creste, modificarile se suprapun – reproiectare tot)

INGINERIA SOFTWARE StSt 5

CURSUL 2- LEGILE LUI LEHMAN

III - Self Regulation

The program evolution process is self regulating with close to normal distribution of measures of product and process attributes

Procesul de evolutie al unui PPSW este autoreglabil, legat de distributia uniforma a

facilitatilor modificate ale PPSW

parametrilor facilitatilor PPSW

(Cantitatea de facilitati se ofera constant in timp)

INGINERIA SOFTWARE StSt 6

CURSUL 2- LEGILE LUI LEHMAN

IV - Conservation of Organisational Stability

The average effective global activity rate on an evolving system is invariant over the product life time.

Activitatea de modificare a evolutiei unui PPSW este constanta in medie

pe tot ciclul de viata al PPSW

(cantitatea de efort organizational se pastreaza)

INGINERIA SOFTWARE StSt 7

CURSUL 2- LEGILE LUI LEHMAN

V - Conservation of Familiarity

During the active life of an evolving program, the content of successive releases is statistically invariant

In ciclul de viata operationala a unui PPSW

continutul nou al versiunilor succesive

este invariant statistic

(cantitatea de nou e constanta)

INGINERIA SOFTWARE StSt 8

CURSUL 2- LEGILE LUI LEHMAN

VI - Continuing Growth

Functional content of a program must be continually increased to maintain user stisfaction over its lifetime

Facilitatile unui PPSW trebuiesc mereu mărite

pentru a mentine satisfactia utilizatorului

cat mai mult timp

(mereu trebuie sa se ofere facilitati in plus sau imbunatatite)

INGINERIA SOFTWARE StSt 9

CURSUL 2- LEGILE LUI LEHMAN

VII - Declining Quality

Programs will be perceived as of declining quality unless rigorously maintained and adapted to a changing operational environment

Se va sesiza descresterea calitatii PPSW

daca nu este bine

mentinut si adaptat

dupa schimbarea environmentului

INGINERIA SOFTWARE StSt 10

CURSUL 2- LEGILE LUI LEHMAN

VIII - Feedback System

Programming Processes constitute Multi-loop, Multi-level Feedback systems and must be treated as such to be successfully modified or improved

Procesul de creare/instalare/operare/mentenanta

e sistem cu multe bucle de reactie

si este el insusi modificabil

pentru a mentine adaptarea

INGINERIA SOFTWARE StSt 11